Deep-frying in oil

Why

In oil heated to about 160–180 °C, the water at the surface of the food turns rapidly into steam that rushes outwards, holding back the fat while the surface dries and sets into a golden crust; in lukewarm oil the steam fades before the crust has set, and the food takes up more fat. Every fat has a smoke point, the temperature at which it begins to give off a bluish smoke: refined oils and frying fats have a high one, unrefined oils and butter a low one, and it drops with every further use because the fat breaks down. How long a fat lasts in the fryer depends more on its resistance to oxidation than on its smoke point; worn-out oil gives itself away by a dark, cloudy colour, an acrid smell, smoke and thickening. For chips and other potato products it is recommended not to exceed 175 °C and to fry only until golden, not brown, because acrylamide rises quickly with higher temperature and darker colour. Water in hot oil boils instantly and spatters the oil, which is why burning fat must never be put out with water.

How to do it

• Fry in a deep fryer or a deep pot; fill the oil only so high that there is room left for it to bubble up once the food goes in, and in a fryer never above the MAX mark.
• Watch the temperature with a thermometer or thermostat; dry the food first and lower it in in small batches, carefully and away from you.
• Never leave frying unattended; as soon as the oil starts to smoke, turn off the heat.
• Cover a burning pot with a lid or baking sheet, turn off the heat and leave it covered until it has cooled; a fire blanket or a class F extinguisher is the backup.
• Never put out burning oil with water or carry the pot anywhere; if the fire doesn't go out at once, leave, close the door behind you and call 112 or your local emergency number (150 in Czechia).
• Strain used oil, store it covered in a cool, dark place and throw it out once it darkens, foams, smells off or smokes at normal frying temperature.

If it goes wrong

Food that has soaked up oil can't be de-greased; let the oil reheat and fry the next batch smaller. If food is burnt outside and raw inside, fry it at a lower temperature next time; thicker pieces can be finished in the oven. If the oil starts to smoke, take it off the heat and let it cool; don't use oil that has smoked heavily for frying again.